1. Field of the Invention
The present invention relates to a focus detection apparatus which performs a camera focus detection arithmetic operation at a high speed, and a control method thereof.
2. Description of the Related Art
There is a TTL phase difference automatic focus detection (auto focus; AF) scheme which leads a light beam transmitted through a shooting lens onto a pair of photoelectric conversion elements and executes a focus detection arithmetic operation based on an output from each photoelectric conversion element to detect a defocus quantity of the shooting lens. This scheme is generally often adopted in a single-lens reflex camera.
Further, multi AF having a plurality focus detection frames is often adopted in recent single-reflex camera, and the number of range finding points is increased.
Therefore, the focus detection arithmetic operation takes time in the arithmetic operation itself. Furthermore, since the number of range finding points is increased, the focus detection arithmetic operation requires a time in units of several-ten ms until the arithmetic operation is completed with respect to all focus detection frames. This leads to an increase in a time lag.
Generally, a focus detection algorithm is configured by using various kinds of arithmetic operation commands (computer programs) of a microcomputer, and the focus detection arithmetic operation is executed based on this focus detection algorithm. In order to reduce a time required for this focus detection arithmetic operation, a speed of an operation clock of the microcomputer is increased, or a high-performance microcomputer is used. However, such an increase in a speed or performance has a limit.